Long answer? It really depends what you want. German breweries use protein rests to control the amount of FAN in their lagers and consequently to control fermentability. See the article on German beers by Dan Gordon in the latest issue of Zymurgy for more information. They are very scientific about it, and adjust the time from 5 to 20 minutes and the temperature from 52 - 62 celsius, so unless you do a lot of trial and error, you'll just be guessing about the effects. But you don't need a protein rest for any highly modified malts, and Golden Promise is one of them.